In a grain silo, the compressor is installed outside the ATEX classified zones, in a separate plant room that is clean and ventilated. Only the compressed air enters the hazardous zones, through pipework, to equipment designed for those zones. The zoning of your site and the approval of the location belong to your safety manager.
For flow sizing across the site, see our page on the compressor for grain silos. This article only deals with location.
Why does the compressor stay outside the zones?
A standard screw compressor, like those in our range, is not equipment intended for classified zones. It combines an electric motor, a controller, a fan and parts that run hot.
It also has a weakness specific to silos: it draws in the air of its room. In air loaded with grain dust, the intake filter clogs, the cooler fouls and the machine overheats. A clean room protects both the site and the compressor.
Where should the plant room be?
A checklist to go through with your safety manager:
- Away from intake pits, elevators, galleries, dust collectors and loading areas.
- A clean air intake, on the side away from dusty areas, with no recirculation of the hot air the machine blows out.
- Ventilated and frost-free, for the compressor and for the dryer.
- Accessible during the season, so the filters can be checked without crossing a zone.
- A three-phase supply close by: the voltage is on each model's data sheet.
Our article on compressor room installation covers ventilation and clearances around the machine.
Taking the air into the zones: sizing the buffer receiver
A distant plant room means a longer network. During a run of cleaning pulses, pressure can drop at the end of the line before the compressor catches up. A buffer receiver close to the users solves this.
The calculation, step by step:
- The flow to cover at the end of the line, Q, in L/min of free air.
- The reserve time you want, t, in minutes.
- The acceptable pressure drop in the receiver, Δp, in bar.
- The volume: V = Q × t ÷ Δp.
Example, figures for guidance only. A dust collector and the cylinders of a tower use 250 L/min together. You want 2 minutes of reserve while the receiver pressure falls from 7.5 to 6.5 bar, so Δp = 1 bar. V = 250 × 2 ÷ 1 = 500 L. Our air receiver size calculator runs this with your own figures.
If the buffer receiver sits inside a classified zone, its drain and accessories must suit that zone: have this validated. A receiver is pressure equipment and subject to inspections: see our guide to air receiver regulations.
Which compressor for this layout?
- Small room, everything built in. The K 75 combines a screw compressor, 420 L receiver, refrigerated dryer and filtration. It delivers 1.1 m³/min at 8 bar.
- A larger site. The K 110 delivers 1.7 m³/min at 8 bar, with a 340 L receiver and built-in dryer.
- A room big enough to separate the parts. The S 110, same flow, with a receiver and dryer chosen for the site.
Pitfalls specific to silos
- Pipework. Lay it with a fall and a drain at the low points, and identify every wall crossing. Our guide to connecting a compressor to the air network shows the layout.
- Equipment inside the zones. Solenoid valves, cylinders and sensors in a zone are chosen for that zone by the plant supplier. The compressor does not qualify them.
- Blow guns. Blowing dust puts it back into the air. Follow your site's cleaning rules.
- Maintenance during the season. Check the intake filter every week. First service at 500 hours, then every 1,500 hours, with a reminder on the controller.
Send the site plan and zoning with a quote request: we propose a location and a buffer receiver for your safety manager to approve.
For your trade: Compressor for grain silos and agricultural cooperatives.